Fire resistant cable with ceramifiable layer

Abstract

A fire resistant cable comprising: a conducting element (2; 21); a layer, surrounding the conducting element, made of a ceramifiable composition comprising: —a thermoplastic polymer mixture comprising: (a) a copolymer of ethylene with a C4-C12 alpha-olefin, having a density of from 0.860 to 0.910 g / cm3, a melt flow index not higher than 3 g / 10 min and a melting point of 105° C. at most; (b) an ethylene homopolymer or copolymer of ethylene with a C4-C12 alpha-olefin, having a density of from 0.900 to 0.985 g / cm3, a melt flow index not higher than 5 g / 10 min and a melting point of at least 110° C.; and (c) a polyethylene grafted with an ethylenically unsaturated monomer; —at least 25 wt % of silica; —a fluxing agent selected from alkaline metal oxides or precursors thereof; —an inorganic hydroxide compound selected from magnesium hydroxide, aluminium hydroxide and mixtures thereof; —a stabilizing agent comprising a hydrated magnesium silicate in an amount of at least 5 wt %; weight percentages being based on the total weight of the ceramifiable composition. Upon exposure to elevated temperatures such as those encountered in case of fire, the ceramifiable composition is transformed into a ceramic material capable of protecting the conducting element from fire and mechanical stresses. The fire resistant cable of the present invention can continue operating under fire conditions for a certain period of time.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to a fire resistant cable for power transmission or for telecommunications. More particularly, the present invention relates to a fire resistant cable which is capable of continuing to operate and maintain circuit integrity for a certain period of time when subjected to fire. The cable of the present invention is also resistant to water and mechanical stresses, such as those caused by the water jets used in fire-extinguishing operations. Also, the present invention relates to a ceramifiable composition suitable for producing said cable.[0002]As known, for example, from IEC 60331 and CEI 20-22 / 2, an energy or data cable resistant to fire (known as a “fire resistant” cable) is a cable configured so as to be capable of continuing to function with acceptable performance even if, owing to a fire, it is exposed to a direct flame for a period of time, at temperatures of up to 800° C.-900° C. or above.[0003]Fire resistant cables...

AI Technical Summary

Benefits of technology

The patent is about a new ceramizable composition that can be used to make cables with good mechanical properties that can withstand fire and other mechanical stresses for a certain period of time. The composition is based on a mixture of specific thermoplastic ethylene polymers and contains silica as a main filler. When exposed to high temperatures, the composition reacts to form a ceramic layer that is resistant to fire and cracks. The manufacturing process is faster and more cost-effective than traditional crosslinked polymer compositions. The composition contains polyethylene grafted with an ethylenically unsaturated monomer to improve its mechanical properties. The use of an amorphous silica powder with substantially spherical particles allows for the easy extrusion of the composition without increasing its viscosity. The fluxing agent in the composition helps to form silicates that reinforce the ceramic layer, resulting in a coherent material that is resistant to fire and mechanical stresses.

Problems solved by technology

The manufacturing of cable layers formed by crosslinked polymers, however, requires a crosslinking step that makes the overall cable manufacturing process rather long and expensive.

However, the mechanical properties of the non-crosslinked thermoplastic materials, especially when charged with inorganic fire-resistant fillers, are too poor to make them suitable materials for manufacturing cable layers.

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